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J Med Chem. 2012 Mar 8;55(5):2406-15. doi: 10.1021/jm201690h. Epub 2012 Feb 16.

Radiosynthesis and evaluation of an (18)F-labeled positron emission tomography (PET) radioligand for brain histamine subtype-3 receptors based on a nonimidazole 2-aminoethylbenzofuran chemotype.

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Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, Building 10, Room B3 C346A, 10 Center Drive, Bethesda, Maryland 20892, USA.


A known chemotype of H(3) receptor ligand was explored for development of a radioligand for imaging brain histamine subtype 3 (H(3)) receptors in vivo with positron emission tomography (PET), namely nonimidazole 2-aminoethylbenzofurans, represented by the compound (R)-(2-(2-(2-methylpyrrolidin-1-yl)ethyl)benzofuran-5-yl)(4-fluorophenyl)methanone (9). Compound 9 was labeled with fluorine-18 (t(1/2) = 109.7 min) in high specific activity by treating the prepared nitro analogue (12) with cyclotron-produced [(18)F]fluoride ion. [(18)F]9 was studied with PET in mouse and in monkey after intravenous injection. [(18)F]9 showed favorable properties as a candidate PET radioligand, including moderately high brain uptake with a high proportion of H(3) receptor-specific signal in the absence of radiodefluorination. The nitro compound 12 was found to have even higher H(3) receptor affinity, indicating the potential of this chemotype for the development of further promising PET radioligands.

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